Can anyone explain how these small bowls work. Mine are mounted directly above engine mounted fuel water separator and have a very small tubular line going from the top to the mechanical fuel pump. Neither of mine have any fuel in them and both appear clean but appear to never have been serviced in any way. Thumbwheel at bottoms are rusted and don’t turn. One engine is very hard to start . Have confirmed spark and air now focusing on fuel. Clean fuel and new filter applied. Don’t have a fuel pressure gauge on board at this time